This invention relates to ridged horns utilized in satellite communications. More particularly, this invention relates to a multi-ridged horn antenna utilizing separate excitation conductors for each ridge, whereby the cross-section of the conductor is chosen to optimize horn performance, and provide high power handling capability.
In the field of satellite communications, antenna systems are required to have a broad bandwidth while having a narrow antenna beam width. The broad bandwidth enables the antenna system to both transmit and receive signals over frequency bands of several GHz. The narrow antenna beam width provides a high gain for signals that are received and transmitted over a particular frequency to and from a particular satellite, and provides discrimination between satellites.
Due to the high speed at which aircraft travel, antenna systems which are mounted on aircraft are required to maintain a low profile. The low profile minimizes drag. Typically, an antenna system is placed within a radome that has a height restriction in the range of 4 inches to 6 inches depending on the type of aircraft. As such, the antenna itself must be very compact and also equally broadband. The focus-fed parabolic reflector antenna may be utilized in such conditions. While the parabolic reflector must be compact so must the feed to avoid excessive aperture blockage of the antenna system. A quad-ridged horn may be utilized in such antenna systems.
The ridged horn antenna is a type of broadband antenna that is often used in communications systems. A ridged horn antenna generally includes ridges which carry electromagnetic energy from the signal source to the aperture area of the ridged horn antenna. An excitation conductor, usually a conductive wire, excites a field between the ridges which ultimately radiates from the horn antenna.
More specifically, a quad-ridged horn is an example of a ridged horn antenna which has a hollow conductive conduit, known as the horn waveguide, usually having a circular square or cross section for propagation of signal waves. The horn waveguide may be formed of an electrically conductive material or of a non-conductive material that is plated or coated with an electrically conductive material. Moreover, to receive signals, horn antennas are dimensioned and flared to receive a concentration of low energy at one or more specific frequencies within the throat area of the horn. A quad-ridge horn is dual-polarized and includes four ridges or tapered ridges which aid in the propagation of the signal waves.
These conventional quad-ridged horns have very limited power dissipation capability due to the small diameter of the wire that excites the fields between the ridges. A problem arises in that a high power signal must be transmitted in many systems, including aircraft applications, which requires high power handling within the quad-ridged horn.
In the prior art, the U.S. Pat. No. 6,154,183, issued to Wolf, teaches a waveguide antenna with a coaxial feed which can be used with both round waveguides and square waveguides. Wolf utilizes these coaxial feeds to improve the electrical power capabilities of the waveguide antenna. Wolf teaches the use of coaxial probes/conductors connected to the coaxial feed which vary in length to adjust the waveguide impedance. However, Wolf does not discuss the use of ridged horn antennas nor does he teach excitation probes which are independently coupled to each ridge.
The U.S. Pat. No. 6,271,799, issued to Rief et al., discloses a dual-polarized quad-ridged antenna horn for small size requirements. Rief teaches a phased array antenna from a plurality of antenna horns connected to a dielectric substrate, whereby the horn axis is orthogonal to the substrate. The antenna horns themselves comprise four spaced apart electrically conductive ridges extending longitudinally on an inner side of an electrically conductive conduit (waveguide). Rief further teaches the use of two feed elements for each quad-ridged antenna horn. Each feed element is positioned on the dielectric substrate orthogonal to the axis. As such, each feed is connected to two opposing ridges. The Rief patent, however, does not teach the use of separate excitation conductors for each ridge. Furthermore, Rief does not teach excitation conductors which extend outwardly from the back of the horn to form a cavity between a matching circuit (or a planar balun) and the back of the horn.
In view of the aforementioned shortcomings, the present invention seeks to provide a quad-ridged horn antenna having excitation conductors driven by a matching circuit which provides high power handling capability while the horn antenna is in operation.
The present invention relates to a ridged feed horn antenna for use in broadband satellite communications. This multi-ridged feed horn operates in a receive band of 10-13 GHz and a transmit band of 14-15 GHz. With the expected antenna data rates being several MBPS. The antenna feed structure must be compact and capable of operating at a very high power. The ridged feed horn antenna comprises excitation conductors which excite the field between each of the ridges in the feed horn antenna. The excitation conductors are connected to each of the ridges and run parallel to the horn axis. A waveguide, terminated at the back of the horn antenna enables the ridges to guide the energy from their respective excitation conductors toward the mouth of the feed horn antenna. A planar balun and matching circuit, located at the back of the horn antenna, may be used to feed each of the excitation conductors. Furthermore, the cross-section of each excitation conductor is chosen so as to optimize horn antenna performance (impedance match bandwidth and power handling). Each excitation conductor extends outwardly from the back of the horn and is parallel to the longitudinal axes of the horn waveguide. Essentially, a dual-ridged feed horn would require two excitation conductors and a quad-ridged feed horn would require four excitation conductors. The excitation conductors form a multiconductor balanced transmission line.
Moreover, the horn antenna includes a cavity to ensure a broad bandwidth match between the excitation conductors and the ridges. The cavity is located between the ridges and a termination wall of the waveguide. This multi-ridged horn antenna, through use of multiple excitation conductors, is capable of handling high levels of power. Problems such as overheating of conductive wires, which have adverse affects on the antenna capabilities, are eliminated by the present invention.
In one aspect, the present invention provides ridged horn antenna, including:
a horn waveguide being an electrically conductive conduit, and the horn waveguide having a first end and a second opposite end along a horn axis, the first end forming a termination wall, and the horn waveguide forming a mouth at the second end,
at least two ridges being spaced apart and extending longitudinally on an inner side of the horn waveguide relative to horn axis and each of the at least two ridges tapering to the mouth of the horn waveguide, the at least two ridges having a 180 degree rotational symmetry, each of the at least two ridges being connected to a corresponding excitation conductor, each excitation conductor extending parallel to the horn axis from the back termination wall to one of the at least two ridges.